This application is based upon and claims priority of Japanese Patent Applications No. 2001-126046, filed in Apr. 24, 2001 and No. 2002-044950, filed in Feb. 21, 2002, the contents being incorporated herein by reference.
1. Field of the Invention
The present invention relates to a semiconductor device provided with a fuse to be disconnected by a laser and to a method of disconnecting a fuse provided on a semiconductor circuit.
2. Description of the Prior Art
As higher performance of semiconductor devices are required in recent years, downsizing and higher integration of elements are accelerated. However, more defects tend to occur as downsizing and higher integration of the elements progress, thus incurring a drop in fabrication yields. In order to avoid the foregoing, a redundant circuit is sometimes provided inside a semiconductor device. The semiconductor device provided with such a redundant circuit is generally designed to use a fuse in order to switch a defective circuit to the redundant circuit.
FIG. 1 is a view showing one example of a method of switching circuits with a fuse.
A redundant circuit 51 has a constitution identical to that of a basic circuit 52. This redundant circuit 51 is connected with a contact point a of a switch circuit 53 and the basic circuit 52 is connected with a contact point b of the switch circuit 53. A center tap c of the switch circuit 53 is connected with a buffer 54. Moreover, a control terminal s of the switch circuit 53 is connected with a node N between a resistor R and a fuse F. The resistor R and the fuse F are serially connected between a power source line Vh and a ground line Vgnd.
When the fuse is not disconnected, the electric potential of the control terminal s of the switch circuit 53 is equal to the electric potential of the ground line Vgnd (which is referred to as a xe2x80x9cLxe2x80x9d level), and the center tap c of the switch circuit 53 is connected with the contact point b. Therefore, the buffer 54 is electrically connected with the basic circuit 52 and electrically separated from the redundant circuit 51.
When the basic circuit 52 is defective, the fuse F is disconnected by a laser. Accordingly, the electric potential of the control terminal s of the switch circuit 53 is made equal to the electric potential of the power source line Vh (which is referred to as a xe2x80x9cHxe2x80x9d level), whereby the center tap c and the contact point a are connected. Therefore, the buffer 54 is electrically connected with the redundant circuit 51 and electrically separated from the basic circuit 52.
In this way, the defective circuit can be switched into the redundant circuit by disconnecting the fuse F by a laser.
FIG. 2 is a cross-sectional view showing a conventional semiconductor device provided with a fuse. An insulating film 62 is formed on a semiconductor substrate 61, and lower wiring including lines 63a and 63b is formed on this insulating film 62. Another insulating film 64 is formed on both of the insulating film 62 and the lower wiring, and a fuse 65 is formed on the insulating film 64. Both ends of this fuse 65 are electrically connected with the lower lines 63a and 63b severally through via contact portions 64a and 64b formed inside the insulating film 64. Another insulating film 66 is formed on both of the insulating film 64 and the fuse 65.
In the semiconductor device thus constituted, a laser is irradiated onto the center portion of the fuse 65 via the insulating film 66 when the fuse 65 is disconnected. In this way, the center portion of the fuse 65 irradiated by the laser is heated up above the melting point thereof and changed from a solid phase to a liquid phase or a gas phase, and a sudden rise of pressure causes a so-called thermal explosion. The fuse 65 is disconnected by this thermal explosion, and a part of the insulating film 66 (an upper part of the disconnected portion of the fuse) is exfoliated as shown in FIG. 3.
The inventers of the present invention perceive that the above-described conventional semiconductor device and the method of disconnecting the fuse bear the following problem.
As described above, the thermal explosion occurs upon disconnecting the fuse 65 by the laser. In this event, large pressure is also applied to the insulating film 64 under the fuse 65, whereby a part of the insulating films 64 and 62 may be exfoliated and a crack may also occur in the insulating film 64 and 62. When damages such as exfoliation or cracks occur in the insulating films 64 and 62, water may easily infiltrate into the semiconductor substrate 61 and a wiring layer, thus causing deterioration of characteristics.
Incidentally, Japanese Patent Laid-Open No. Hei 9 (1997)-36234 discloses a fuse, which is composed of first and second fuse elements disposed vertically via an insulating film, and a contact portion which connects tip portions of these first and second fuse elements electrically. Moreover, Japanese Patent Laid-Open No. Hei 9 (1997)-36234 also discloses a fuse, in which the first and the second fuse elements are formed in the same layer, whereby the fuse is composed by electrically connecting the first and the second fuse elements with the contact portion. These fuses are designed as surely disconnectable by irradiating a laser onto the contact portion.
Meanwhile, Japanese Patent Laid-Open No. Hei 4 (1992)-14245 discloses a fuse composed of a partially thinned aluminum line, in which a member easily heated by a laser (a heating member) such as a polysilicon film is disposed under the fuse. According to the publication, the fuse made of aluminum can be surely disconnected by means of heating the heating member by the laser to cause thermal explosion.
However, the fuses disclosed in those publications cannot yet avoid damages on insulating films under the fuses upon disconnection.
An object of the present invention is to provide a semiconductor device and a method of disconnecting a fuse capable of reducing damages on an insulating film under a fuse upon disconnecting the fuse by a laser.
A semiconductor device according to the present invention includes a semiconductor substrate, an insulating film formed on the semiconductor substrate, a fuse formed on the insulating film, and a protective member formed stronger than the insulating film and disposed under a disconnecting point of the fuse.
In the semiconductor device of the present invention, the high-strength protective member is disposed under the disconnecting point of the fuse. When a laser is irradiated on the disconnecting point of the fuse, the temperature at the disconnecting point is suddenly increased and thermal explosion occurs. In this event, the protective member protects the lower insulating film, whereby occurrence of damages such as exfoliation and cracks can be prevented. Moreover, as the thermal explosion occurs on the high-strength protective member, destructive pressure is concentrated on an upper side of the protective member. In this way, the fuse can be efficiently disconnected. In addition, a form of destruction of the fuse is also stabilized.
Only one protective member may be disposed per fuse, or a plurality of protective members may be also disposed. Moreover, in the case of a semiconductor device provided with a plurality of fuses, it is preferable that the fuses are arrayed within a certain area in consideration of operating efficiency upon disconnection of the fuses.
A method of disconnecting a fuse according to the present invention is a method of disconnecting a fuse of a semiconductor device including a semiconductor substrate, a first insulating film formed on the semiconductor substrate, wiring formed on the first insulating film, a second insulating film formed on the first insulating film and the wiring, a fuse formed on the second insulating film, and a via contact portion formed inside the second insulating film to connect the fuse and the wiring electrically, in which the fuse is disconnected by irradiating a laser onto a connective portion of the fuse to the via contact portion.
According to the present invention, the via contact portion is also used as the protective member, whereby the fuse is disconnected by irradiating the laser onto the connective portion of the fuse to the via contact portion. In this way, the via contact portion protects the insulating film under the fuse, whereby occurrence of damages such as exfoliation and cracks can be prevented.
Moreover, another method of disconnecting a fuse according to the present invention is a method of disconnecting a fuse of a semiconductor device including a semiconductor substrate, a first insulating film formed on the semiconductor substrate, wiring formed on the first insulating film, a second insulating film formed on the first insulating film and the wiring, a fuse formed on the second insulating film, a via contact portion formed inside the second insulating film to connect the fuse and the wiring electrically, and a plurality of protective members formed stronger than the second insulating film and disposed separately from one another under the fuse, in which the fuse is disconnected by severally irradiating a laser onto at least one of portions directly above the protective member out of a plurality of the protective numbers.
According to the present invention, the plurality of protective members are provided under the fuse. Then, upon disconnection of the fuse, the laser is irradiated onto upper portions of these protective members. In other words, the fuse is disconnected at a plurality of portions. In this way, the fuse can be surely disconnected. Moreover, upon irradiation of the laser, each of the protective members protects the insulating film under the fuse, whereby occurrence of damages such as exfoliation and cracks can be prevented.
The fuse may be also disconnected by irradiating the laser onto a portion between the protective members. In this case, the insulating film under the fuse is also protected by the respective protective members, whereby occurrence of damages such as exfoliation and cracks can be prevented.